To add to the op's comments. Missing elements of a wall or watchtower are from my experience due to that part of the structure colliding. It could a branch or the limbs of a dead tree that are hitting the part of the proposed structure that cannot be built. I suggest that successful placement of a fence and watchtower kit should only happen if the structure can be built in it's entirety i.e. should it not be possible to build any part of the structure then placement should happen.

To add to the op's comments; I have had similar issues. Build parts of both fences and walls are not always possible to construct, sometimes it might a lower part of a wall, sometimes the upper. It would make a lot more sense if the fence and watchtower kits only allowed successful placement if the structure can be built in it's entirety.

tested on 0.61.138602, fails to render as per original report

Issue persists 0.61.138602

Can not clean rags with alcohol tincture 0.61.138602

Ok I'll try to upload directly... http://i1279.photobucket.com/albums/y540/Kemps7/20160628120958_1_zpszaeeqh5q.jpg

Ooops, I forgot the screenshot..